Vehicular sub-frames are well known in the art. An example of such sub-frames is disclosed in Japanese Patent Laid-Open Publication No. HEI 4-232183 entitled “SUSPENSION CROSS MEMBER FOR VEHICLE”. The disclosed suspension cross member is used to mount a generally A-shaped suspension arm to a front frame of a vehicle body therethrough. The cross member has an arm securing portion extending therefrom. The arm securing portion has a reinforcing member provided thereon. The suspension arm is supported by the reinforcing member.
The suspension arm is made from light metals such as aluminum alloy for reduction in weight. Since the arm securing portion itself provides insufficient strength, the reinforcing member serves to reinforce the arm securing portion of the cross member.
These types of vehicular sub-frames should provide strengths sufficient to mount such vehicle components as suspensions to vehicle bodies. It is preferred for these sub-frames to be partly increased in strength because they are undesirably increased in weight if strengthened throughout.
For the cross member as disclosed in the aforementioned publication, the separate reinforcing member of steel is provided to achieve the increased strength of the arm securing portion of the cross member. This increases the number of parts of the cross member. The cross member having such an additional reinforcing member is manufactured at a higher cost.
Moreover, a joining process such as welding or casting would be necessarily performed if the reinforcing member needs to be firmly joined to the A-shaped suspension arm. Such a joining process is, however, undesirably costly to perform.
FIG. 8 hereof shows in plan a conventional sub-frame 101 mounted to a vehicle body (not shown). The sub-frame 101 includes horizontal members 121, 121 and vertical members 122, 122. Similarly to the cross member as discussed above, the sub-frame 101 is used in mounting to the vehicle body a vehicle component such as a suspension. Additional projecting portions 102, 102 are provided in place on the sub-frame 101. The projecting portions 102, 102 are to be mounted to an exhaust pipe 103 through a band 104 and a bolt 105. The sub-frame is usually produced by subjecting blanks to press working and then welding them together. However, the press working and the subsequent welding are not suitable for producing the sub-frame with improved efficiency. Moreover, the press working and welding is undesirably costly to perform. To address these problems, casting is often used in producing the sub-frames. The use of the casting enables the sub-frames to be produced in large amounts.
With respect to FIG. 9 hereof, a lost foam pattern made from expandable resin is shown as being buried or embedded in sand 115. The pattern has formed therein a gate 111, runners 112, 112 communicating with the gate 111, a cavity 113 communicating with the runner 112, and gas vents 114, 114 communicating with the cavity 113. Molten metal 116 is poured into the cavity 113 through the gate 111 and the runners 112, 112, after which the pattern is melted and vaporized by the heat of the molten metal to provide a desired casting for use as a sub-frame. Rather than the pattern, metal molds are more preferably used to facilitate producing the sub-frame in large amounts. Because the casting does not involve the press working and welding as discussed above, the sub-frame can be produced with improved efficiency.
Referring to FIG. 10 hereof, there is shown the pound sign-shaped or number sign-shaped (hereinafter #-shaped) cavity 113 having recessed portions 117, 117 communicating therewith. The four runners 112 extend from the gate 111 to the cavity 113. If poured into a metal mold having the cavity 113 thus arranged, the molten metal flows slowly into the recessed portions 117, 117. The molten metal within the recessed portions 117, 117 is then cast into the projecting portions to be mounted to vehicular components.
It is desirable to use die casting rather than the above-mentioned casting so as to ensure that the sub-frame provides increased strength. Die casting machines are designed such that molten metal is forced into cavities formed in the die casting machines at a high pressure and speed to thereby provide a die casting of dense cast structure. Use of the die casting is advantageous because the resultant die cast sub-frames are lightweight and thin.
In producing the #-shaped sub-frame using a die casting machine having formed therein the cavity 113 as shown in FIG. 10, the molten metal flows at a very high speed within the cavity. Thus, misrun could be undesirably produced throughout the resultant die cast sub-frame. In addition, the molten metal would cause unwanted eddies or vortexes when flowing into the recessed portions 117, 117. The die casting is therefore less frequently used for producing the sub-frame.